1. Field of the Invention
The present invention relates to a photosensitive composition having a good storage stability and a high sensitivity.
2. Description of the Related Art
Heretofore, various image forming methods have been known in diazo-process photography. Examples of these methods include: dye-imaging, which utilizes photodecomposition of an aromatic diazo compound, such as a diazonium salt, a diazo sulfonate, or a diazo compound, for example, an iminoquinone diazide, a naphthoquinone diazide, or the like, together with a coupling agent according to need; preparation of printing plates, proofs, mask films, and the like by utilizing a hardening reaction or a solubilization phenomenon; and foam imaging.
As to photopolymerization, in the field of preparation of materials for printing plates, proofs, mask films, photoresists, and the like, there have been known various image forming methods which utilize changes in properties, such as solubility, tackiness, adhesion, and the like due to a photochemical hardening reaction.
In the diazo-process photography, the amount of energy required for photodecomposition of a photodecomposable aromatic diazo compound to be used is generally very large and sensitive wavelengths extend into a visible blue light region. Consequently, the scope in which diazo-process photography can be used is limited to materials that have a low sensitivity and are printed by ultraviolet light. In order to solve this problem, intense studies have been conducted regarding spectral sensitization of photodecomposable aromatic diazo compounds in a visible light region. As a result, some specific dyes, such as riboflavin, porphyrin, chlorophyll, and the like, are now known to act as spectral sensitizers for diazonium salts and diazo sulfonates. As another example of the sensitization method, Japanese Patent Application Publication (JP-B) No. 50-21,247 discloses a photosensitive material for diazo-process photography wherein the photosensitive composition comprises an aromatic diazo compound together with at least one compound selected from the group consisting of a sulfinic acid and a salt of sulfinic acid in combination with a sensitizing dye.
However, none of these methods of prior art have been put to practice, because these methods are associated with drawbacks, for example, poor stability and restricted scope of selectivity in spectral wavelength regions. Further, these systems have little or no effect in the spectral sensitization for the photodecomposition of diazo compounds such as naphthoquinone diazides.
Despite continuous development of new spectrally sensitizing technologies for photopolymerization, the region of spectral wavelengths that can be used in prior art is still up to 500 nm, and therefore a system, that can be spectrally sensitized in a wavelength region ranging from 500 nm to infrared light and has a high sensitivity and good stability has not been put to practical use.
As a candidate that may overcome the above-mentioned drawbacks, Japanese Patent Application Laid-Open (JP-A) No. 62-143,044 discloses a photopolymerization initiator comprising a cationic dye/borate anion complex. This system can be spectrally sensitized freely in a region ranging from blue light to infrared light, has good stability, and exhibits a high level of sensitivity. However, since the sensitivity is several mJ/cm.sup.2, the sensitivity needs to be upgraded before the system is put to practical use.
As stated above, a truly satisfactory system, which has a good storage stability and a high sensitivity, has not been proposed in either diazo-process photography or photopolymerization.